1. Field of the Invention
The present invention relates to a phosphor-containing film containing phosphors that emit fluorescence upon irradiation with excitation light and a backlight unit including the phosphor-containing film as a wavelength converting member.
2. Description of the Related Art
Applications of a flat panel display such as a liquid crystal display (LCD) (hereinafter, also referred to as “LCD”) as a space-saving image display device with low power consumption have been widespread year by year. In recent liquid crystal displays, further power saving, an enhancement in color reproducibility, or the like is required as an improvement in LCD performance.
Along with power saving of LCD backlight, in order to increase the light utilization efficiency and improve the color reproducibility, it has been proposed to use a wavelength converting layer containing a quantum dot (QD, also referred to as a quantum point) that converts a wavelength of incident light and emits the wavelength-converted light, as a luminescent material (phosphor).
The quantum dot is a state of an electron whose movement direction is restricted in all directions three-dimensionally. In the case where nanoparticles of a semiconductor are three-dimensionally surrounded by a high potential barrier, the nanoparticles become quantum dots. The quantum dot expresses various quantum effects. For example, a “quantum size effect” is expressed in which a density of electronic states (energy level) is discretized. According to this quantum size effect, the absorption wavelength and luminescence wavelength of light can be controlled by changing the size of a quantum dot.
Generally, such quantum dots are dispersed in a resin or the like, and used as a quantum dot film for wavelength conversion, for example, by being disposed between a backlight and a liquid crystal panel.
In the case where excitation light is incident from a backlight to a film containing quantum dots, the quantum dots are excited to emit fluorescence. Here, white light can be realized by using quantum dots having different luminescence properties and causing each quantum dot to emit light having a narrow half width of red light, green light or blue light. Since the fluorescence by the quantum dot has a narrow half width, wavelengths can be properly selected to thereby allow the resulting white light to be designed so that the white light is high in luminance and excellent in color reproducibility.
Meanwhile, there are problems that quantum dots are susceptible to deterioration due to moisture or oxygen, and particularly the luminescence intensity thereof decreases due to a photooxidation reaction. Therefore, the wavelength converting member is configured in such a manner that gas barrier films are laminated on both main surfaces of a resin layer containing quantum dots (hereinafter, also referred to as a “quantum dot layer”) which is a wavelength converting layer containing quantum dots, thereby protecting the quantum dot layer.
However, merely protecting both main surfaces of the quantum dot layer with gas barrier films has a problem in which moisture or oxygen enters from the end face not protected by the gas barrier film, and therefore the quantum dots deteriorate.
Therefore, it has been proposed to protect the entire periphery of the quantum dot layer with a barrier film.
For example, JP2010-061098A discloses a quantum dot wavelength converting structure including a wavelength converting portion containing quantum dots for wavelength-converting excitation light to generate wavelength-converted light and a dispersion medium for dispersing the quantum dots, and a sealing member for sealing the wavelength converting portion, in which the wavelength converting portion is disposed between two sealing sheets which are sealing members, and the peripheries of the wavelength converting portion in the sealing sheets are heated and thermally adhered to each other, thereby sealing the wavelength converting portion.
Further, JP2009-283441A discloses a light emitting device including a color conversion layer (phosphor layer) for converting at least a part of color light emitted from a light source portion into another color light and a water impermeable sealing sheet for sealing the color conversion layer, and discloses a color conversion sheet (phosphor sheet) in which penetration of water into the color conversion layer is prevented by a configuration where the sheet has a second bonding layer provided in a frame shape along the outer periphery of the phosphor layer, that is, so as to surround the planar shape of the color conversion layer, and the second bonding layer is formed of an adhesive material having water vapor barrier properties.